1 Chronicles 23:2-5, 28-31

At the same time he brought together all the leaders of Israel, the priests, and the Levites. The Levites thirty years and older were counted; the total was thirty-eight thousand. David sorted them into work groups: “Twenty-four thousand are in charge of administering worship in the sanctuary; six thousand are officials and judges; four thousand are security guards; and four thousand are to serve in the orchestra, praising GOD with instruments that I have provided for praise.”

From now on the assigned work of the Levites was to assist Aaron’s sons in the work of worship in GOD’s house: maintain courtyards and closets, keep the furniture and utensils of worship clean, take care of any extra work needed in the work of worship, and provide bread for the table and flour for the Meal Offerings and the unraised wafers—all baking and mixing, all measuring and weighing. Also they were to be present for morning prayers, thanking and praising GOD, for evening prayers, and at the service of Whole-Burnt-Offerings to GOD on Sabbath, at New Moons, and at all festivals. They were on regular duty to serve GOD according to their assignment and the required number.